1. Field of the Invention
The embodiments relate to back end of the line (BEOL) processing of semiconductor wafers and, more specifically, to a contact formation method that incorporates a preventative etch step for reducing interlayer dielectric material (e.g., borophosphosilicate glass (BPSG)) flake defects.
2. Description of the Related Art
Current back end of the line (BEOL) contact formation techniques and, more specifically, current BEOL tungsten (W) plug formation techniques can result in the flaking of borophosphosilicate glass (BPSG) interlayer dielectric material at the edge of a semiconductor wafer and, thereby can result in surface defects. More particularly, tungsten (W) is commonly used to fill contact openings, which extend vertically through a BPSG layer to a semiconductor substrate. Tungsten (W) is typically deposited by chemical vapor deposition (CVD) using tungsten hexafluoride (WF6) gas. Unfortunately, WF6 gas can also etch any exposed semiconductor material within the contact openings. To avoid such etching, a protective liner is deposited in the contact openings prior to tungsten (W) deposition. While this protective liner is generally sufficient to protect the semiconductor material within any contact openings that are patterned above the center portion of the substrate, oftentimes it is insufficient to protect the semiconductor material within contact openings that are patterned above the edge portion of the substrate (i.e., near the wafer's edge). As a result, the semiconductor material within the contact openings near the wafer's edge is etched, creating voids and undercutting the BPSG layer. Such voids reduce BPSG layer adhesion, causing BPSG flaking and, thereby creating surface defects.
Therefore, there is a need in the art for a back end of the line (BEOL) processing technique that prevents contact level defects and, more particularly, a BEOL processing technique that prevents BPSG flaking, which creates contact-level surface defects.